Desirable Measurement on Accurate Hysteresis Curve for Large Nd–Fe–B Sintered Magnets at Elevated Temperatures

摘要

To obtain an accurate hysteresis curve in large Nd-Fe-B sintered magnets at elevated temperatures, we compared the hysteresis curves obtained from the following methods: a superconducting magnet-based vibrating sample magnetometer (SCM-VSM) and the hysteresis graph (HG). Attention was paid to the values of dJ/dH near H_cJand Hk/H_cJ, where J, H, H_cJ, and H_kare the magnetization, the magnetic field, coercivity, and knee field, respectively. In the HG method, greater dimensional ratio (L/D) led to easier uniform magnetization of cylindrical magnets, causing larger L/D to improve dJ/dH near H_cJand H_k/H_cJ. However, the magnetization distortion did not appear at all in the SCM-VSM method at various temperatures and, thus, we could measure the values of dJ/dH near H_cJand H_k/H_cJas well as the hysteresis curve exactly.